Add a specialized apps::NativeAppWindow for app_shell

apps/apps_client.h

Index: apps/apps_client.h
diff --git a/apps/apps_client.h b/apps/apps_client.h
index f67aad679c7f3b1af3035e7e4d1ccb0999735722..26b6c42442c2ffe18440360e3ff486d640d6cdd5 100644
--- a/apps/apps_client.h
+++ b/apps/apps_client.h
@@ -17,6 +17,8 @@ class Extension;
 
 namespace apps {
 
+class ShellWindow;
+
 // Sets up global state for the apps system. Should be Set() once in each
 // process. This should be implemented by the client of the apps system.
 class AppsClient {
@@ -29,6 +31,17 @@ class AppsClient {
   virtual bool CheckAppLaunch(content::BrowserContext* context,
                               const extensions::Extension* extension) = 0;
 
+  // Creates a new apps::ShellWindow for the app in |extension| for |context|.
+  // Caller takes ownership.
+  virtual ShellWindow* CreateShellWindow(
+      content::BrowserContext* context,
+      const extensions::Extension* extension) = 0;
+
+  // Tells the embedding application to stay running. The application may close
+  // after a matching number of calls to EndKeepAlive() are made.
+  virtual void StartKeepAlive() = 0;
+  virtual void EndKeepAlive() = 0;
+
   // Return the apps client.
   static AppsClient* Get();